The present invention relates to a tensioning device which is used to select and impart a moment of torque to a shaft. The present tensioning device has been found to be particularly useful in connection with conveyor belt cleaners which utilize scraper blades to clean a conveyor belt.
Conveyor belt cleaning devices typically include a shaft which is positioned transverse to the direction of conveyor belt travel and one or more scraper blades mounted on the shalt. When the shaft is rotated, the blades are forced into engagement with the conveyor belt such that the blades will scrape adherent material from the belt. The scraper blades wear during use such that the scraper blades contact the belt with a continually diminishing force, and may entirely lose contact with the belt, thereby hampering the scraper blades' cleaning ability. The shaft on which the scraper blades are mounted must therefore be rotated as the blades wear to reposition the scraper blades against the conveyor belt with the desired amount of force.
Torsional tensioning devices of the type shown in U.S. Pat. No. 5,149,305 have been used in connection with conveyor belt cleaners. In this prior device an operator rotates a worm by hand with an Allen wrench to impart rotational bias to the conveyor belt cleaner shaft. In this device the worm is coupled directly to the shaft such that any rotation of the shaft will result in a corresponding rotation of the worm about the longitudinal axis of the shaft. Such an arrangement exposes the operator to potential injury. Scraper blades are subjected to repeated impact forces which are generated by the blades coming into contact with conveyor belt splices and with enlarged pieces of the conveyed material or other material which adheres to the belt, all of which may cause sudden rotation of the shaft. In addition the conveyor belt itself may grab the scraper blades causing a large sudden rotation of the shaft. In the prior device such shaft rotations are directly transmitted to the operator through the corresponding rotation of the worm about the axis of the shaft and may potentially cause injury to the operator. Such arrangements in the past have resulted in injuries to operators when the operator is applying a wrench to the drive member and a splice is encountered by the cleaner blades, and when a wrench is inadvertently left on the drive member and comes flying off upon a sudden rotation of the shaft.